The effect of RF on Partial thickness defect of articular cartilage. In this project, RF energy will be applied to the partial thickness defects of articular cartilage. SEM will be used to evaluate the ultrastructure of collagen on cartilage surface. We are studying the effect of radiofrequency energy on joint cartilage with partial thickness defect. The cartilage matrix is composed of a concentrated solution of proteoglycan entrapped within a dense network of collagen fibrils. If one ingredient changes its concentration or structure, the whole network may fail and cause articular cartilage defects and degenerative joint disease. We hypothesize that Radiofrequency (RF) energy will shrink the collagen in a partial thickness articular cartilage defect and melt the surface collagen resulting in less fibrillation and cartilage degeneration long term. For this research program, we will perform two studies using sheep stifle joints. In a first study we will determine the optimal RF temperature. Chondrocyte viability will be analyzed by confocal microscopy (calcein AM, EthD- 1). In a second study we will keep RF temperature constant and vary sacrificing time. Chondrocyte viability, histological and biochemical parameters will be analyzed long term.